全文获取类型
收费全文 | 567211篇 |
免费 | 6234篇 |
国内免费 | 1006篇 |
专业分类
电工技术 | 10511篇 |
综合类 | 466篇 |
化学工业 | 90138篇 |
金属工艺 | 23339篇 |
机械仪表 | 18510篇 |
建筑科学 | 12542篇 |
矿业工程 | 4313篇 |
能源动力 | 14441篇 |
轻工业 | 45802篇 |
水利工程 | 6947篇 |
石油天然气 | 14963篇 |
武器工业 | 39篇 |
无线电 | 60303篇 |
一般工业技术 | 116317篇 |
冶金工业 | 95664篇 |
原子能技术 | 14682篇 |
自动化技术 | 45474篇 |
出版年
2021年 | 5490篇 |
2019年 | 5274篇 |
2018年 | 9210篇 |
2017年 | 9415篇 |
2016年 | 9840篇 |
2015年 | 6033篇 |
2014年 | 10254篇 |
2013年 | 26140篇 |
2012年 | 15798篇 |
2011年 | 21114篇 |
2010年 | 16998篇 |
2009年 | 18836篇 |
2008年 | 19095篇 |
2007年 | 18795篇 |
2006年 | 16310篇 |
2005年 | 14764篇 |
2004年 | 14032篇 |
2003年 | 13709篇 |
2002年 | 13260篇 |
2001年 | 12858篇 |
2000年 | 12335篇 |
1999年 | 12019篇 |
1998年 | 27677篇 |
1997年 | 20049篇 |
1996年 | 15635篇 |
1995年 | 12011篇 |
1994年 | 10863篇 |
1993年 | 10616篇 |
1992年 | 8336篇 |
1991年 | 8103篇 |
1990年 | 7993篇 |
1989年 | 7764篇 |
1988年 | 7479篇 |
1987年 | 6749篇 |
1986年 | 6535篇 |
1985年 | 7390篇 |
1984年 | 6702篇 |
1983年 | 6437篇 |
1982年 | 5779篇 |
1981年 | 5896篇 |
1980年 | 5630篇 |
1979年 | 5735篇 |
1978年 | 5664篇 |
1977年 | 6179篇 |
1976年 | 7686篇 |
1975年 | 5108篇 |
1974年 | 4903篇 |
1973年 | 4980篇 |
1972年 | 4281篇 |
1971年 | 4038篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
J. M. Kremer A. A. Shabana G. E. O. Widera 《International journal for numerical methods in engineering》1993,36(1):17-42
This investigation concerns itself with the computer implementation of the dynamic formulation of thin laminated composite plates consisting of layers of orthotropic laminae that undergo large arbitrary rigid body displacements and small elastic deformations. A finite element preprocessor computer program is developed to automatically generate the invariants of the laminae, which may have arbitrary orientations. The laminae invariants are then used to obtain the invariants of the elements and the composite laminated plate. The consistent and lumped mass formulations of the invariants of motion of composite plates are compared and it is concluded that the two methods are comparable, if a fine enough finite element mesh is used. The structure of the dynamic equations of motion, based on the formulation presented in Part I of this paper, is examined. Non-linear centrifugal and Coriolis forces arising as the result of the finite rotations of the laminae are defined, and the solution schemes of the resulting non-linear differential equations of motion are discussed. Numerical examples illustrating the differences between homogeneous isotropic and laminated composite plates are presented. An RSSR (Revolute-Spherical-Spherical-Revolute) mechanism is used in the numerical examples, with the coupler modelled as a laminated plate flexible body. It is found that the inertia of the plate contributed greatly to the transverse deformation. The effects of laminae orientation is also investigated. 相似文献
992.
Shoulder pain secondary to impingement of the rotator cuff tendons underneath the coracoacromial arch is a common problem seen in athletes who perform repetitive overhead activities. Shoulder impingement has been classified into primary and secondary types. Several factors contribute to impingement, including rotator cuff weakness, posterior capsule tightness, and subacromial crowding. Recently, it has been proposed that scapulothoracic muscle weakness could be a factor that contributes to impingement. Traditional rehabilitation protocols for shoulder impingement syndrome stress individualized rotator cuff strengthening. The authors propose that individualized scapulothoracic muscle strengthening should be a part of any protocol for nonoperative treatment of secondary shoulder impingement syndrome. 相似文献
993.
A hitherto unavailable analytical solution to the free vibration problem of general cross-ply laminated rigidly clamped rectangular plates, incorporating first-order shear deformation, and rotatory and in-plane inertias into the formulation, is presented. A recently developed boundary continuous displacement-based generalized Navier solution technique is used to solve the five highly coupled linear second-order partial differential equations with constant coefficients, and the associated geometric boundary conditions. The assumed solution functions are in the form of double Fourier series, which satisfy the rigidly clamped boundary conditions a priori in a manner similar to the conventional Navier method. Convergence characteristics of the natural frequencies of both symmetric and antisymmetric cross-ply plates are numerically established. Other numerical results presented herein include (i) comparison with the corresponding available first-order shear deformation theory-based Galerkin and classical lamination theory-based boundary-discontinuous analytical solutions, and (ii) study of the effects of thickness and aspect ratio on the natural frequencies. 相似文献
994.
995.
OD de Rada AC Villaro LM Montuenga A Martínez DR Springall JM Polak 《Canadian Metallurgical Quarterly》1993,162(1-2):121-124
The presence of nitric oxide synthase (NO-synthase), the enzyme responsible for the production of nitric oxide (NO) from L-arginine, is shown immunocytochemically in the intrinsic neurons of the human and porcine respiratory tract. NO-synthase immunoreactivity is demonstrated in a subpopulation of neurons of the microganglia present in the wall of the extra- and intrapulmonary bronchi as well as in the hilar region of the lung in relation to blood vessels. The immunostaining was also found in some nerve fibers of the respiratory nervous system. Human and porcine lung gave similar results. The possible involvement of NO in the nonadrenergic noncholinergic (NANC) nervous regulation of the lung is discussed. 相似文献
996.
Electronic BITE is poor at identifying hardware failure and in present design approaches tends to create the reviled ‘unconfirmed failure’. A different approach to BITE and unconfirmed failure could improve both operational performance and the cost of maintenance. 相似文献
997.
998.
Kelly Jeffrey A.; Murphy Debra A.; Sikkema Kathleen J.; Kalichman Seth C. 《Canadian Metallurgical Quarterly》1993,48(10):1023
Behavior change remains the only means for primary prevention of HIV disease. Psychology should take a leading role in efforts to curtail the epidemic, but has not contributed to HIV prevention at a level proportionate to the urgency of the crisis. The authors propose an updated agenda for behavioral research on AIDS-HIV prevention implementing accelerated community trials of promising behavior change models, conducting trials of community-level interventions on a large scale and focused on populations most vulnerable to HIV infections, establishing partnerships between HIV research and community service organizations, integrating efforts from across psychology disciplines to advance and refine HIV prevention interventions, and mobilizing interdisciplinary HIV prevention resources and communication mechanisms to rapidly translate research findings to community and public policy arenas. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
999.
1000.
We report 11 patients having revision of total hip arthroplasty using massive structural allografts for failure due to sepsis and associated bone loss. All patients had a two-stage reconstruction and the mean follow-up was 47.8 months (24 to 72). Positive cultures were obtained at the first stage in nine of the 11 patients, with Staphylococcus epidermidis being the most common organism. The other two patients had draining sinuses with negative cultures. There was no recurrence of infection in any patient. The mean increase in the modified Harris hip score was 45 and all the grafts appeared to have united to host bone. Two patients required additional procedures, but only one was related to the allograft. Complications included an incomplete sciatic nerve palsy and one case of graft resorption. Our results support the use of massive allografts in failed septic hip arthroplasty in which there is associated bone loss. 相似文献